1. Field of the Invention
The present invention relates to an ink jet recording head ejecting ink droplets to a recording material to form an image, an ink jet recording apparatus and a process for producing the head.
2. Description of the Related Art
In recent years, an ink jet recording apparatus is receiving attention as a color recording apparatus of high quality in spite of the low cost thereof. As an ink jet recording head for an ink jet recording apparatus, for example, a piezoelectric ink jet recording head ejecting an ink from a nozzle by pressure generated by mechanical deformation of a presser chamber with a piezoelectric material, and a thermal ink jet recording head ejecting an ink from a nozzle by pressure generated by evaporation of the ink caused by electrification applied to heater elements arranged on respective flow paths have been known.
As a currently available thermal ink jet recording head, ink jet recording heads disclosed in JP-A-9-226142 (hereinafter referred to as Conventional Example 1), JP-A-10-76650 (hereinafter referred to as Conventional Example 2), and JP-A-9-327921 (hereinafter referred to as Conventional Example 3) have been known.
The ink jet recording head of Conventional Example 1 will be described below with reference to FIGS. 23 to 26B. FIG. 23 is a perspective view showing an example of an ink jet recording head and an ink supplying member carried on a conventional ink jet recording apparatus. FIG. 24 is a cross sectional view on line B—B in FIG. 23.
As shown in FIGS. 23 and 24, a head chip 200 has plural respective flow paths 202 formed therein, and nozzles 204 for ejecting an ink are formed on the tip ends thereof. The plural respective flow paths 202 are connected to a common liquid chamber 206 inside the head chip. Heater elements 208 are provided on the mid flows of the respective flow paths 202, an ink in the respective flow paths 202 in contact with the heater elements 208 is bubbled with heat from the heater elements 208, whereby ink droplets are ejected from the nozzles 204 by pressure obtained by the bubbling to carry out recordation. The common liquid chamber 206 has an ink supplying inlet 210 for supplying the ink from the outside.
An ink supplying member 212 is arranged on an upper part of the heat chip 200. The ink supplying member 212 has an ink flow path 214 for supplying the ink from an ink tank (not shown in the figure) to the head chip 200. On the mid flow of the ink tank and the ink supplying member 212 (ink flow path 214), a filter (not shown in the figure) is arranged to filter minute solid matters in the ink to prevent invasion of minute solid matter into the head chip 200, whereby clogging of the nozzles is prevented.
The head chip 200 is formed by conjugating a flow path substrate 220 having the respective flow paths 202, the common liquid chamber 206 and the like formed therein and a heater element substrate 226 having the heater elements 208 formed therein.
A process for producing the head chip 200 configured as in the foregoing will be described with reference to FIGS. 25A to 25F.
The heater element substrate 226 can be produced, for example, by using the production technique and the production apparatus for an LSI. On a single crystal silicon wafer 228, a heater layer forming the heater elements, and a protective layer for preventing the heater elements 208 from breakage by pressure of the bubbles thus formed are formed (as shown in FIG. 25A). A signal line for supplying electric power and signals to the heater layer from the outside is connected thereto. Driver circuits 224, signal processing circuits 222 and external signal input and output terminals 227 are similarly formed for the plural heads. A resin layer 230 formed, for example, with photosensitive polyimide, is accumulated as a protective layer to an ink (as shown in FIG. 25B).
The flow path substrate 220 can be produced by forming, on a silicon wafer 232, grooves 233 and 235 forming the common liquid chambers 206 and the respective flow paths 202 by orientation dependent etching (as shown in FIGS. 25C and 25D). As the method for forming the grooves 233 and 235 by orientation dependent etching, as shown in JP-A-6-183002, an etching mask is patterned on a silicon wafer having a <100> crystalline plane as a surface, and etching is carried out by using a heated potassium hydroxide (KOH) aqueous solution. The grooves 233 and 235 to be the common chambers 206 and the respective flow paths 202 formed by using the orientation dependent etching become grooves having desired angles.
After coating an adhesive to the silicon wafer 232, the two silicon wafers 228 and 232 are conjugated with accurate positioning with positioning marks 234 (as shown in FIG. 25E). Thereafter, the silicon wafers thus conjugated are cut and separated into a dice form along dicing lines 237, for example, by a method disclosed in Japanese Patent No. 2,888,474, to produce plural head chips 200 at the same time (as shown in FIG. 25F). The tip ends of the flow paths 202 are opened by cutting to form the nozzles 204 ejecting ink droplets.
Thereafter, the head chip 200 is fixed on a heat sink 236 for heat dissipation as shown in FIGS. 23 and 24. The heat sink 236 also has a printed circuit substrate 238 formed thereon, whereby electric power and signals supplied to a main body of the ink jet recording apparatus are transmitted to the heater element substrate 226, and at the same time, signals of various sensors provided on the heater element substrate 226 are transmitted to the main body of the ink jet recording apparatus.
An ink is supplied from an ink tank to an ink jet recording head 244 thus produced. The ink supplied from the ink tank runs in the ink flow path 214 inside the ink supplying member 212 to reach the common liquid chamber 206 inside the head chip 200 through the ink supplying inlet 210 opened on an upper part of the flow path substrate 220 of the head chip 200, and then supplied to the respective flow paths 202, whereby ink droplets are ejected from the nozzles 204 with the heater elements 208.
In recent years, however, an ink jet recording apparatus is demanded to have high resolution and small dots for attaining high image quality, and the dimensions of the respective flow paths 202 and the nozzle 204 of the head chip 200 are considerably decreased associated with the demands. The thus narrowed respective flow paths 202 are easily clogged with a small foreign matter that has not caused any problem to cause a critical printing defect, i.e., dot missing. In order to attain such high resolution at a printing speed that is equivalent to or higher than the conventional products, the number of nozzles per chip head is necessarily increased, and the increase of the nozzles also lowers the reliability of the ink jet recording head. In other words, the unitary reliability of the nozzle is necessarily increased by a large margin in order to maintain and improve the reliability of the ink jet recording head.
Under the circumstances, JP-A-2001-246758 proposes a measure for preventing the clogging by providing fine filters in the vicinity of inlets of the respective flow paths in addition to the filter provided on the mid flow of the ink tank and the ink supplying member 212. The filters adjacent to the respective flow paths exert a considerable effect for preventing the clogging. However, when a large amount of foreign matters are trapped at the filter, the supply of the ink to the corresponding respective flow path 202 is impaired because the filter is positioned adjacent to the respective flow path, whereby such a problem is caused that the ink discharging (printing) performance is lowered. Thus, there is room for improvement in the case of an ink jet recording head that is used for a long period of time.
FIGS. 26A and 26B show the improved head chip proposed in JP-A-2001-246758, in which FIG. 26A is a plane view showing the flow path part of the head chip, and FIG. 26B is a cross sectional view thereof. That is, a filter 250 is formed in such a manner that columnar bodies are formed at positions with a prescribed interval inside the common liquid chamber 206 with a certain distance from the respective flow paths 202 rather than at the inlets of the respective flow paths 202. In this case, even when the filter 250 catches a foreign matter, an ink is supplied to a respective flow path 202A through a space between the filter 250 and the respective flow paths 202, and thus the ink is discharged from a nozzle 204A (as shown by the arrows in FIG. 26A). However, when a large amount of foreign matters 252 are caught in the direction aligning the respective flow paths 202, the supply speed of the ink cannot follow the printing speed to cause defects, such as thin spots upon continuous printing.
Furthermore, the discharging direction of ink droplets is largely affected by defects, such as cracking of the nozzle part, that are allowed in the conventional products, and thus there is an increased demand for the quality of the nozzles.
Moreover, the depth of the common liquid chamber of the conventional inkjet recording head is determined by the thickness of the silicon wafer and is about from 500 to 600 μm. On the other hand, because the groove depth of the miniaturized respective flow paths is about 10 μm, the ink flow rate is considerably slowed down in the common liquid chamber, and there are such regions where the ink is substantially not moved (dead water regions) in some locations. Therefore, when a gas dissolved in the ink forms bubbles due to temperature change, the bubbles stay in the regions with no flow and grow therein. At this time, the growing bubbles in the ink jet recording head 200 are large due to the large capacity of the common liquid chamber 206. Therefore, they cause serious printing defects due to inhibition of supply of an ink to the respective flow paths 202, and the aspiration amount of the ink upon removing the bubbles by aspirating the ink from the nozzles 204 is increased, whereby they cause not only deterioration in ink using efficiency but also deterioration in total printing speed.